The CAF-1 and Hir Histone Chaperones Associate with Sites of Meiotic Double-Strand Breaks in Budding Yeast.

Brachet E, Béneut C, Serrentino ME, Borde V - PLoS ONE (2015)

Bottom Line:
Nucleosomes may represent an obstacle for the recombination machinery and their timely eviction and reincorporation into chromatin may influence the outcome of recombination, for instance by stabilizing recombination intermediates.Here we show in budding yeast that nucleosomes flanking a meiotic DSB are transiently lost during recombination, and that specific histone H3 chaperones, CAF-1 and Hir, are mobilized at meiotic DSBs.This study is the first example of the involvement of histone H3 chaperones at naturally occurring, developmentally programmed DNA double-strand breaks.

ABSTRACTIn the meiotic prophase, programmed DNA double-strand breaks (DSB) are introduced along chromosomes to promote homolog pairing and recombination. Although meiotic DSBs usually occur in nucleosome-depleted, accessible regions of chromatin, their repair by homologous recombination takes place in a nucleosomal environment. Nucleosomes may represent an obstacle for the recombination machinery and their timely eviction and reincorporation into chromatin may influence the outcome of recombination, for instance by stabilizing recombination intermediates. Here we show in budding yeast that nucleosomes flanking a meiotic DSB are transiently lost during recombination, and that specific histone H3 chaperones, CAF-1 and Hir, are mobilized at meiotic DSBs. However, the absence of these chaperones has no effect on meiotic recombination, suggesting that timely histone reincorporation following their eviction has no influence on the recombination outcome, or that redundant pathways are activated. This study is the first example of the involvement of histone H3 chaperones at naturally occurring, developmentally programmed DNA double-strand breaks.

pone.0125965.g007: Recombination in CAF-1 mutants does not rely more of the class II crossover pathway.DSB formation and CO frequency at HIS4LEU2 in mms4 slx4 yen1 triple mutant (VBD1444) and in mms4 slx4 yen1 cac1Δ (VBD1443) monitored by Southern blot. The graph shows DSB and CO quantification from the same time-courses.

Mentions:
Then we asked if the absence of crossover reduction in cac2Δ cells could be because a weakening of the ZMM-dependent pathway could be compensated by an increased use of the class II crossover pathway. To test this hypothesis, we examined crossovers in CAF-1 mutants also deficient for the three nucleases known to promote the class II CO pathway, namely Mus81-Mms4, Slx1-Slx4 and Yen1 [6]. As previously described, the inactivation of these three nucleases reduced CO frequency at HIS4LEU2, by 40% [6]. However, the combined deletion of CAC1 did not further reduce CO formation (Fig 7). We independently confirmed this observation, by showing that interference, which is promoted by the class I CO pathway, was not altered in the cac1Δ mutant (Table 1).

pone.0125965.g007: Recombination in CAF-1 mutants does not rely more of the class II crossover pathway.DSB formation and CO frequency at HIS4LEU2 in mms4 slx4 yen1 triple mutant (VBD1444) and in mms4 slx4 yen1 cac1Δ (VBD1443) monitored by Southern blot. The graph shows DSB and CO quantification from the same time-courses.

Mentions:
Then we asked if the absence of crossover reduction in cac2Δ cells could be because a weakening of the ZMM-dependent pathway could be compensated by an increased use of the class II crossover pathway. To test this hypothesis, we examined crossovers in CAF-1 mutants also deficient for the three nucleases known to promote the class II CO pathway, namely Mus81-Mms4, Slx1-Slx4 and Yen1 [6]. As previously described, the inactivation of these three nucleases reduced CO frequency at HIS4LEU2, by 40% [6]. However, the combined deletion of CAC1 did not further reduce CO formation (Fig 7). We independently confirmed this observation, by showing that interference, which is promoted by the class I CO pathway, was not altered in the cac1Δ mutant (Table 1).

Bottom Line:
Nucleosomes may represent an obstacle for the recombination machinery and their timely eviction and reincorporation into chromatin may influence the outcome of recombination, for instance by stabilizing recombination intermediates.Here we show in budding yeast that nucleosomes flanking a meiotic DSB are transiently lost during recombination, and that specific histone H3 chaperones, CAF-1 and Hir, are mobilized at meiotic DSBs.This study is the first example of the involvement of histone H3 chaperones at naturally occurring, developmentally programmed DNA double-strand breaks.

ABSTRACTIn the meiotic prophase, programmed DNA double-strand breaks (DSB) are introduced along chromosomes to promote homolog pairing and recombination. Although meiotic DSBs usually occur in nucleosome-depleted, accessible regions of chromatin, their repair by homologous recombination takes place in a nucleosomal environment. Nucleosomes may represent an obstacle for the recombination machinery and their timely eviction and reincorporation into chromatin may influence the outcome of recombination, for instance by stabilizing recombination intermediates. Here we show in budding yeast that nucleosomes flanking a meiotic DSB are transiently lost during recombination, and that specific histone H3 chaperones, CAF-1 and Hir, are mobilized at meiotic DSBs. However, the absence of these chaperones has no effect on meiotic recombination, suggesting that timely histone reincorporation following their eviction has no influence on the recombination outcome, or that redundant pathways are activated. This study is the first example of the involvement of histone H3 chaperones at naturally occurring, developmentally programmed DNA double-strand breaks.